[PATCH] ide: explain the PCI bus test we do in <asm-i386/ide.h>

Matthew Wilcox asked that this got a comment explaining why it is done
so here it is.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/asm-i386/ide.h b/include/asm-i386/ide.h
index 79dfab87135d..454440193eac 100644
--- a/include/asm-i386/ide.h
+++ b/include/asm-i386/ide.h
@@ -41,6 +41,12 @@ static __inline__ int ide_default_irq(unsigned long base)
 
 static __inline__ unsigned long ide_default_io_base(int index)
 {
+        /*
+         *      If PCI is present then it is not safe to poke around
+         *      the other legacy IDE ports. Only 0x1f0 and 0x170 are
+         *      defined compatibility mode ports for PCI. A user can 
+         *      override this using ide= but we must default safe.
+         */
         if (pci_find_device(PCI_ANY_ID, PCI_ANY_ID, NULL) == NULL) {
                 switch(index) {
                         case 2: return 0x1e8;